The present invention relates in general to duplicative terrestrial digital audio broadcasting systems such as an in-band on-channel (IBOC) hybrid digital and analog radio system, and, more specifically, to controlling a data display of a radio receiver to display program data.
A duplicative radio broadcast system simultaneously transmits 1) a primary channel having at least a main program content and preferably including a supplemental data stream, and 2) a backup channel with main program content that is at least a partial duplicate of the main program content in the primary channel but usually without all or part of the supplemental data stream. Certain differences in the backup channel transmission allow it to be received by a receiver under conditions in which the primary channel is unreceivable.
To accomplish a transition from traditional analog AM and FM broadcast radio services to terrestrial digital audio broadcasting (DAB), hybrid systems are being employed so that existing analog receivers can continue to receive the broadcasts while new digital receivers can be used to receive a higher quality digital signal that is simulcast with the analog signal. In the IBOC hybrid system, both the digital and analog signals are contained within the allocated frequency range of a particular broadcasting station. Typically, the analog signal is transmitted in a center portion with the digital signal occupying upper and lower sideband portions within the range.
Due to differences in transmission power levels, propagation, and performance in fringe areas, the coverage area of the analog signal within which a useful signal can be received is typically larger than the coverage area for the digital signal. Because of this difference in coverage area and because not all broadcasting stations will add digital technology at the same time, digital receivers are designed to receive in either a digital mode or an analog mode. A digital receiver uses the digital signal as its primary channel and the analog signal as a backup channel for receiving a particular broadcast. When both a digital and an analog signal are received, the receiver may blend in a continuous manner from the digital signal to the analog signal (i.e., add the signals in relative proportion to their quality) when the quality of the digital signal deteriorates.
Eventually, hybrid IBOC stations may transition to an all digital broadcast while retaining the duplicative nature of the broadcast signal (i.e., both the primary and backup channels are digital). In the all digital duplicative system, the backup channel transmits at a lower effective data rate and can be received during times that (or at a place where) the primary channel is impaired. In order to achieve a lower data rate, all or part of the supplemental data and possibly some portion of the main program content are omitted from the backup channel (e.g., by encoding the main audio program at a lower bit rate).
In addition to improved signal quality, a digital broadcast enables the transmission of supplemental digital data along with the main audio program of a radio broadcast. The supplemental digital data may include program data (PD) which relates to the main audio program or may include auxiliary data services. As used herein, program data includes any program data services such as station identification or conventional program-associated data (PAD) or any other auxiliary data that may be broadcast for providing information to a user of a receiver. When the main audio program includes music selections, for example, conventional PAD may include song title, artist, genre, album, or other song information. Such data is communicated (i.e., displayed) to the radio user on a graphical or text display integrated with the receiver or may be reproduced (i.e., displayed) as spoken audio using a text-to-speech converter. The program data may also include text messages during other broadcast segments such as commercial messages and talk segments.
When the digital signal in the primary channel is impaired or not available for any reason, the radio receiver blends to or entirely switches over to the analog or digital signal in the backup channel. Once a good signal is present again in the primary channel, the receiver will blend back to the primary. When the digital signal is impaired and the backup channel analog signal is utilized, at least a portion of the program data will no longer be received. In prior art radio receivers, data is processed in real time and typically appears in the display only for as long as the data is being received. Thus, when the digital transmission is lost, program data being displayed may disappear even though the main audio program continues to play. A radio listener may see a song title or artist name being displayed at one moment and then have no information or a blank display at the next moment if blend to analog has occurred. However, the radio listener would prefer the data display to be continuous and not be intermittent depending on signal conditions.